There are many situations in industry where it is necessary to provide backup electrical power for emergency situations. In nuclear reactors, hospitals, computer and communication centers and anywhere that reserve power is needed, banks of batteries are being installed to provide that reserve power. Of course, the reserve power must be able to survive any condition which would cause the primary power to fail.
Not only are these reserve power systems intended for use when primary power sources shut down, they are intended to be able to provide power under any condition. In the industry, they are termed Uninterruptable Power Supply (UPS) systems. The fact telephone service remained intact immediately after the Oakland earthquake during the Baseball World Series several years ago is a testimonial to the existence of UPS systems. The tragedy at Chernobyl in the former Soviet Union is an example of where a UPS system failed, actually causing further injury and damage as communications and relief efforts were delayed by the lack of back up or reserve power.
Frames for UPS systems have two requirements. First, the frames must be able to support a bank of batteries, usually in a two tier configuration, without transfer of electrical power except upon demand. Second, the frames must withstand severe seismic shock such as that experienced in explosions, heavy storms such as hurricanes, and, most importantly, in earthquakes of significant magnitude.
Conventional systems for providing UPS systems has been to construct steel frames, which have appropriate insulation. These frames are intended to survive the aforementioned forces. Typical systems include two or more frames which are, perhaps, 60 inches high. Cross braces are placed between them to make a frame or rack for the heavy storage batteries. There is a need to insulate the frame to prevent discharge of the reserve power and potentially harmful currents being present.
UPS system frames have to survive substantially intense tests. One such test includes the inducement of simulated earthquake conditions. In this test, a frame is placed on a ten foot by fifteen foot table, and loaded with up to 12,000 pounds of batteries. The table is shaken at the specific G factor and frequency which simulates an earthquake of a specific magnitude, up to and including major forces of Richter scale 7 or more. Actual stress to which the frames are subjected is measured in Hz. It has been learned that subjecting frames to a natural frequency of 6 to 7 Hz will, when forces of 5 G or more are present, cause failure in conventional designs. Present day frames are unfortunately not able to pass this test, but rather collapse in a crumble of twisted steel and crashing batteries. At present, no frame device for UPS systems has passed the more critical tests of this type.
Mere selection of strong steel for the frame structure is not enough. The system is only as good as the frame and the structural steel has to perform. Prior art designs have taken square welded tube, such as 3 inch square tube, at the vertical members and have used shipping car channels welded together as cross pieces. Such a construction requires an extensive amount of welding, which is imprecise and which does not by itself provide a sufficiently rigid structure so as to eliminate harmonic resonance with the test conditions.
Many of the structures which have been proposed require considerable welding to fabricate the design. Even though these designs have not met the required criteria, they are still quite expensive to produce as they are labor intensive. Systems proposed to modify or strengthen these welded systems have not been found to improve the stability of the frames under stress. Merely, the cost is increased.
Accordingly, it is an object of this invention to provide a frame device suitable for holding a large quantity of batteries in a virtually failure proof state so as to provide an uninterruptable power supply.
Another object is to provide a frame for auxiliary power supply which is capable of eliminating harmonic resonance under greater than 5 G gravity at less than 6 to more than 7 Hz frequencies.
Still another object of the present invention is to provide a frame device which eliminates substantial welding while increasing the strength and vibration resistance of the frame.
Other objects will appear hereinafter.